Today I launched my new website, Star Observer, a website dedicated to the observation of stars and open clusters. I created this website to have a more structured way to present my observing reports from my favorite objects: stars and open clusters. At the core of Star Observer you will find a new and growing collection of visual observing reports. There is a separate page for every object observed. On an object's page you will find my personal observing report, a sketch (or image) and some notes and background information about the object. The observing reports can be found in the top bar menu under "Single and multiple stars" and "Open clusters". In the section "observing stars" you will find some information about the equipment and resources I use for planning, executing and evaluating my observations.

In the future new observing reports will be added on a regular bases. I am also planning to publish a few articles about stars and clusters, and the method I developed for planning, executing and evaluating / publishing my observations.

You can navigate through StarObserver.eu using the different menus or the sitemap. If you have any questions or suggestions, please feel free to contact me, using the contact form.
Updates on StarObserver.eu will be announced in this blog. Follow this link to go to the homepage of Star Observer.

It's been a long time since you heard from me, but during the last few months I've been working on a new website dedicated to the observing of stars and star clusters. It will take a little while before it will go online, but I will let you know! In the meantime I'm working on the design and content for this new site, and every now and again I look outside, and wow, in the last week of January Venus and the Moon were lined up in the evening sky. Hope you like the images. Please click to enlarge.

At the moment I'm testing my new camera, the DMK 21AF04 AS. I first tried the camera on the Coronado PST, and I was surprised by the result. The first image is a typical frame I selected from the 1-minute movie I shot from a prominence. The second image shows the stacked (600 frames) and processed version.

I will inform you about the equipment set-up and the stacking/processing software in the near future. Right now I'm busy reading the software manuals and experimenting with the few movies I recorded. In the end this monochrome camera will be used to shoot detailed images of the Moon, the Sun in combination with the Baader Herschel Prism/Continuum filter and the Sun in H-Alpha with the Coronado PST. I will keep you updated!

I would like to thank Jim Kaler (Prof. Emeritus of Astronomy, University of Illinois), for helping me with my “spectral riddle” in NGC 6910, the Rocking Horse cluster. Here’s why the B1 supergiant looks yellow visually instead of bluish-white what you would expect from a B-type star.

As you know it is in the middle of Cygnus, near Gamma Cygni, not far off the galactic plane (you can see my wide angle picture at http://www.astro.uiuc.edu/~kaler/sow/sadr.html). As such it is subject to a great deal of interstellar extinction and reddening from interstellar dust. The dust selectively absorbs and scatters blue light (roughly 1/wavelength), so when you look at a star thru dust it will appear redder than it really is (basically the same reason the sun is reddened at sunset). The intrinsic B-V color of a B1.5 Ia supergiant is -0.2. The observed color is 0.83, about the color of a K0 dwarf or a G5 giant, so the star appears yellowish to the eye.

The whole cluster is highly reddened in fact by about the same amount. The “color excess” (E) is the observed minus true color, which is about 1.0 for this cluster. The absorption at V is usually taken as 3.2E, so Av (abs at V) is 3 magnitudes. If there were not dust, a 7th magnitude star would appear 4th magnitude, and the cluster would be visible to the naked eye. Good observing on your part to notice that. You can see the effect in many other distant clusters near the galactic plane.

In the night of July 13th/14th 2008 I had a short observing session with the 300mm Dob. I took a quick peek at a few old friends (M27, M29, the Blinking Planetary and 16 Cygni) trying out my new 35mm Panoptic. While sweeping through Cygnus, I noticed a bright, small clump of stars North-Northeast of Gamma Cygni. It was very easy to spot with the 35mm Panoptic. I increased the power to 230x with the 7mm Pentax XW, and I was looking at a wonderful little asterism of stars that, as a group looked like a little dog or horse. I made a rough sketch of this object, and when I later checked the sketch with my planetarium program (Voyager), it proved to be NGC 6910, an open cluster from the Herschel 400 list. According to some sources on the Internet, NGC 6910 is also called the Rocking Horse cluster. I had never heard about it or observed it before, so my first impression that it looked like a dog or horse, was not that strange. Others thought of it as a little horse as well.

Where can you find NGC 6910? The map below should give you a rough idea. Just center your telescope on Gamma Cyngi and move just about half a degree north-northeast. There you will find this nice clump of stars.

When you start looking for NGC 6910, bear in mind that it is a small cluster, only 7' in diameter, but then again, at lowest magnification it jumped out at me in my 12-inch scope. With the 22mm Nagler (fov 68') I already saw the complete outline of the little horse, and with the 7mm at 230x I could see a few dimmer, magnitude 12 stars. NGC 6910 is a Y-shaped cluster oriented northwest southeast. I counted between 20 and 25 stars but its always difficult to tell which do belong to the cluster and which are not included. The two brightest stars looked definitely yellow and are from the 7th magnitude.
There is however something that riddles me about these two yellow suns. According to all planetary programs and Internet databases, the Northernmost of the two stars is SAO 49556, a spectral type K1III, which explains the yellowish color. The southernmost of the two is SAO 49563 (or V2118 Cygni), a variable star of spectral type B1.5Ia. Normally I would think that a B1 star shines Bluish or at least mainly white, and not yellow. I checked other observing reports and I found that Sue French's (Celestial Sampler, page 132) reports:

At 87x, two yellowish stars of 7th magnitude and a pearly, split chain of eight 10th magnitude stars unite in a Y-shaped pattern about 5' long.

Sue sees two yellow stars as well, so I'm very curious why this B1 star seems to appear yellow instead of white. Does it have something to do with the Variable character of the star? Maybe one of you out there can help on this one.

Anyway, visually it is a very interesting group, so I made a sketch. The sketch below was made with the 300mm dob, a 7mm eyepiece (fov 18') giving a magnification of 230x. South is up and west is to the left. The next time when you're in the area observing, check out on NGC 6910 and let me know which colors you could see.

About one and a half years ago I bought a 12-inch telescope for deepsky observing, an f/5.3 Newtonian telescope from Orion optics UK. The tube is mounted on a dobsonian rocker-box and equipped with the Argo Navis Digital Telescope Computer. During the past 18 months I have put together my set of eyepieces for this telescope. I had four major criteria for selecting the eyepieces:

1. High quality
2. Large true fields of view
3. Weight between 400 and 800 grams
4. Lots of eye-relief

All selection criteria were important, but the most important was number four, eye-relief. In this article I will tell you why these criteria were more or less important to me, which eyepieces I finally chose and why I chose them.

1. High Quality
I wanted high quality eyepieces, for two reasons. The first reason was that good eyepieces stay with you forever, even when you buy and sell telescopes in the future, the eyepieces stay with you. The second reason was I had the money for buying them.

2. Large true fields of view
If you have a push-to telescope (you follow the object by pushing the telescope manually) you want fields of view that are as large as possible. The higher the magnification the more important this becomes. If for instance you watch the Eskimo Nebula at a magnification of 600x, it virtually flies through your field of view, so the larger the field of view is, the longer you can concentrate on observing before having to move the telescope again.

When I bought the Orion Optics 12-inch, I only had a set of Vixen lanthanum LV eyepieces with an apparent field of view of 50 degrees. Compare that to a Pentax XW eyepiece with a field of view of 70 degrees, you will see that the Pentax's field of view is twice as big, in other words, at the same focal length and magnification, it will take an object twice as long to cross the field of view when using a 70 degree eyepiece instead of a 50 degree eyepiece. So I was looking for high-quality eyepieces with large fields of view. These two criteria already narrowed the search down to Televue Naglers and Panoptics, Pentax XW's or Vixen Lanthanum LVW's.

3. Weight
The Orion-Optics UK dobsonian is a lightweight instrument. I wanted eyepieces that were in more or less the same weight-class to prevent problems with balancing the scope and adding an optional friction brake, which has to be adjusted when switching eyepieces of different weight. So I wanted eyepieces that weighed between 400 and 800 grams.

4. Eye-relief
The last criterion for me was the most important, lots of eye-relief. I always observe wearing glasses. First of all, I have astigmatism. The Televue Dioptrx was no option for me. I tried one for a while, but they can only be used on Televue eyepieces. On top of that, every time I want to look in my star-atlas or make a sketch of the object, I have to put on my glasses anyway, so I want to keep them on all night while observing. With glasses you need eyepieces with lots of eye-relief, preferably 17mm or better (some people find 15mm also OK).

The four criteria narrowed down the search, and in fact only a handful of eyepieces met all my wishes. So in the end, the choice wasn't that difficult at all.

The set of eyepieces I chose

In the first column you will find the eyepieces I chose for my Orion Optics 300mm Dobson. In the second column you see the apparent field of view in degrees, in the third column the magnification of the eyepiece when used in combination with my 12-inch f/5.3 telescope (focal length 1600 mm), in the fourth column the true field of view in arc minutes and in the last column the eye relief in millimeters.

The 35mm panoptic is the eyepiece with the lowest magnification and a large field of view. The three Type 4 Naglers are for medium magnifications. The three Pentax XW's are for high power viewing.

Why I chose these eyepieces

The 35mm Panoptic

This eyepiece is for low power viewing. When searching for objects or observing large objects, this is my favorite eyepiece. The 35mm Panoptic is a wonderful eyepiece. The views of larger objects like the double cluster in Perseus or the Rosette Nebula are simply stunning. A flat field of view with sharp and crisp images.

Another candidate for low power was the 31mm Nagler, but it was too heavy for this telescope and the eye-relief was not as good as with the 35mm Panoptic (19mm vs. 24mm). The true field of view however is a bit wider in the 31mm Nagler.

The 22mm, 17mm and 12mm Nagler Type 4

These eyepieces really surprised me. The first I bought from this series was the 12mm. At first light a had a lot of problems with the kidney-bean effect, large blackout areas, due to the fact that my eye was placed at the wrong position. But once I understood how to use the adjustable eye-cap, I was completely convinced that this eyepiece would stay.

The 12mm Nagler Type 4 produces very bright and clear images, and the field of view is simply overwhelming. It really looks like you are in space. It is not possible to take in the whole field of view at once. You have to move your eye around more or less to look around the rim of the field of view. The spacewalk experience with this 12mm Nagler Type 4 convinced me completely and without hesitation I ordered the 17mm and 22mm Naglers Type 4 as well. These three eyepieces are at the core of my set of eyepieces for my 300mm Dobson and they are the most used magnifications. They are simply wonderful. Open clusters like M 35 or M 37or the Orion Nebula with the 22mm, M81 and M82 with the 17mm, M13 with the 12mm, it al looks just right.

Other eyepieces I tried in the 22-12mm range were the 24mm Panoptic and the 22mm Panoptic (smaller eye-relief and smaller field of view than the Naglers) , the 21mm Denkmeier (smaller field of view, but a very good eyepiece), 17mm Panoptic (poor eye-relief) and the 13mm Type 6 Nagler poor eye-relief, kidney bean effect, pin-cushion distortion).

The 7mm, 5mm and 3.5mm Pentax XW

For high power viewing, the Pentax XW eyepieces are the only high-quality eyepieces with an eye-relief of 20mm and a field of view of 70 degrees. Of course the Nagler Type 6 have a much wider field of view, but the eye relief again is rather poor. It is possible to use eyepieces with an exit-pupil smaller than 2mm without glasses, and still get a sharp image, but as I said before, I want to be able to read, write and draw at the telescope, so I want to keep on my glasses. That's why I chose the Pentax XW over the Naglers in this range. The adjustable eye-caps make me decide for the Pentax over the Vixen LVW eyepieces, which are also very fine, with their 20mm eye-relief and 66 degree field of view. With the Pentax's adjustable eye cap it is possible to adjust the position of the eye, making it easy to take in the whole field of view without getting the kidney-bean effect. It is possible to take in the whole field of view at once. For planetary nebula, small galaxies, globular clusters and double stars, these eyepieces provide the high magnification, but of course to seeing has to be stable to use the high powers.

Conclusion

The choice of this set of eyepieces for this particular telescope was based on my personal wishes (criteria 1-4) and I only can say that all the eyepieces I've tried, were of an excellent quality. Often it was eye-relief that tipped the balance in favor of a certain eyepiece. If you do not wear glasses, the range of eyepieces to choose from becomes much wider. The best advice I can give you is that when you have the chance, try out the different eyepieces before buying them. Also try to write down the things you expect from your eyepieces (price, weight, focal length, eye-relief, which telescope etc.) This will narrow down the number of eyepieces to choose from. In the end the right choice will give you a lot of satisfaction when using them, and probably save you some money as well. Should you have any questions about the eyepieces or my telescope, please feel free to contact me.

On the evening of May 9th 2008 Leo and I got together to observe a series of double stars in Bootes, inspired by an article in June's Sky and telescope (Binaries in your Bootes). In the period between the beginning of May and the end of July it doesn't get really dark at night, but for observing double stars or asterisms, this proved to be not a problem at all. We started at 23.00 hours local time (UT + 2hrs). In three hours time we observed and sketched about six doubles in Bootes and two asterisms, one in Bootes (Picot 1), the other in Ursa Major (Ferrero 6).

The highlight for me that night was Xi Bootes. This colorful double lies about 8 degrees east of Arcturus. The Yellow primary star shines at magnitude 4.8 and it's magnitude 7.6 orange companion lies at a position angle of 315°. The separation is 6.3". Through the 17mm Nagler the double looks fairly close (scale from "Double Stars for small Telescopes" by Sissy Haas). When looking at Xi Bootes through the 17mm Nagler, the double seems to be part of an asterism that looks like the constellation Cygnus, only much smaller. Xi Bootes is placed at the position of Deneb, the tail of the swan. We decided to call the asterism "Little Cygnus". On the sketch below the asterism is oriented West-East. At the tail you find Xi Bootes. Three white stars oriented north-south represent the wings of the little swan. A white star to the east (accompanied by a dimmer companion) is at the position of the head of the swan. The yellow star to the eastern edge of the field of view is just a bright field star. It is no part of the "Little Cygnus" asterism.

The sketch of "Little Cygnus " and Xi Bootes was made using the 300mm f/5.3 Dobson and a 17mm Type4 Nagler. The magnification is 94x and the field of view is 52'. At the telescope I made a sketch on white paper using a HB led-pencil. This sketch was scanned and processed in Photoshop. I colored the double star (and the field star to the east) using the tutorial described on the website of Jeremy Perez ( http://www.perezmedia.net/beltofvenus ). This is the first time I experimented with this technique, and I am very pleased with the result. It produces a realistic image and resembles what you see through the eyepiece. In the future I will try to use this technique for sketching more double and multiple stars.